1. Field of the Invention
The present invention relates to a color image forming apparatus which forms a color image, in particular, to an improved processing control technique of image data.
2. Description of Related Art
In the field of image forming apparatus, such as a color copy machine, color page printer, etc., which performs color printing by one page through the electronic photographic method, as one of the color printing methods, the four-rotation method is known. According to the four-rotation method, one printing unit, which consists of a photosensitive member, a toner drum, etc., is provided, whereby element colors such as, yellow (Y), magenta (M), cyan (C), and black (B) are sequentially transferred on a intermediate transfer member until transfer with respect to all the element colors is completed; and after completing the transfer on the intermediate transfer member, the image carried on the intermediate transfer member is transferred on a piece of paper, whereby color printing is performed. Under this method, transfer of each element color onto the intermediate transfer unit is performed in a manner that the transferring operations do not overlap one another in terms of timing as shown in FIG. 4, that is, after completing transfer of an element color, the transfer of the next element color is started.
As an image processing control mechanism which realizes the printing according to the above-mentioned four rotation method, the mechanism shown in FIG. 5 conventionally is known. According to this type, with respect to one element color, one pair of a RAM/register unit and image processing unit is provided (that is, four pairs are provided in the entire apparatus), transfer of each element color is performed by the pair associated with the element color. However, due to the configuration in which one picture image processing unit is provided with respect to each element color; when an element color is transferred, the other image processing units associated with the other element colors are not used. Thus, this type is problematic in that there is a redundancy in the constitution, so that a useless production cost is generated.
As an image processing mechanism of the other types which solves the redundancy of the constitution, the image processing mechanism shown in FIG. 6 is known. According to this type, only one pair of RAM/register unit and a image processing unit is provided, and changing of element color to be transferred is executed by rewriting the stored contents in the RAM/register unit. However, this type is problematic in that the rewriting requires a predetermined time, so that the printing speed is slowed down, and then the apparatus cannot cope with the recent tendency that high-speed printing is demanded. In particular, this problem has become noticeable these days because there is a tendency that the color images are becoming of high-quality which increases the data amount required for image processing and consequently elongating the rewriting time.